Membrane immunoglobulins of spontaneous B lymphomas of aged BALB/c mice

Four cell lines derived from spontaneous BALB/c B lymphoma tumors were analyzed with regared to the type of their membrane immunoglobulins (Ig). Using lactoperoxidase iodination of membrane proteins combined with immunoprecipitation and electrophoresis on polyacrylamide gel, three of these cell lines (X16c, L10A and K46) were found to express the monomeric form of IgM and IgD as well as half molecules. One cell line (M12) lacked both IgM and IgD. The apparent mol. wt. of the lymphoma μ chain was about 80000 and exceeded the mol. wt. of 75 000 determined for μ chains secreted by myeloma cells. The mol. wt. of the δ heavy chain was found to be 66000. Immunofluorescence showed that the L10A and X16c lines expressed λ light chains on their cell surface. Another Ig‐bearing cell line (K46) expressed both λ and χ chains. Thus, three out of the four B lymphomas examined expressed both IgM and IgD with light chains of the δ type. These results, together with our previous findings which demonstrate the presence of Ia and Fc receptors on the same cells, indicate that spontaneous B lymphomas in BALB/c mice are the malignant counterpart of mature B lymphocytes.